Japanese Patent Application Publication No. 2005-58733 (Patent Document 1) and Japanese Patent Application Publication No. 2007-89650 (Patent Document 2) propose an exercise assisting apparatus wherein a thigh muscle group is tensed and relaxed with hardly any extension of the knee, by displacing a seat with the user's feet resting on a foot supporting surface and the user's buttocks supported on a contact surface of the seat. This exercise assisting apparatus varies the user's weight acting on the user's legs by changing the ratio of the user's weight supported by a seat by displacing the position of the seat.
By an operation of this kind, the load is reduced compared to a case where the whole weight acts on the user's legs, and the thigh muscles are contracted with hardly any extension of the knee, whereby, for example, even a user having knee pain such as a patient with diabetes is able to strengthen the muscle group of the thigh, and furthermore since the muscle group of the thigh has a large volume, it is also expected to obtain a contribution to improvement in lifestyle-related diseases, by glucose metabolism associated with the muscular contraction. Moreover, by using a drive source to displace the seat, the user is able to exercise passively without exerting muscular force spontaneously, and therefore the load is light and consequently the apparatus can be used even by person's having a low capacity of movement.
Incidentally, an exercise assisting apparatus having the composition described above tenses and relaxes the thigh muscle group by changing the weight of the user that acts on the user's legs, with virtually no extension of the knees, and therefore the knee bending angle is an important factor in performing exercise effectively. As the analogy of a squatting movement readily shows, the load acting on the muscle group of the thigh varies with the knee bending angle. Furthermore, in the case of a user with knee pain, if a load acts on the user's knee while the knee is bent to a certain degree, the user often experiences pain and the bending angle must be restricted in order to make an apparatus usable by persons of this type as well.
At the present time, experimental results have been obtained indicating that the exercising effect is high and knee pain is not liable to occur, if the knee bending angle (in practice, the measured angle is that formed between the thigh and the lower leg on the front side of the knee) is set to 140 degrees, and hence this angle has been set as an appropriate angle.
In the apparatus described in Patent Document 2, it is proposed that the position of the seat is made adjustable in such a manner that the knee bending angle becomes the appropriate angle, and the position of the seat is adjusted automatically in accordance with an input parameter relating to the user's height. The position of the seat is adjustable in at least one of the vertical direction and the forward/rearward direction, and the horizontal distance from the foot position becomes greater if the seat is raised, while the horizontal distance from the foot position becomes smaller if the seat is lowered.
Patent Document 2 describes making the knee bending angle adjustable to an appropriate angle by adjusting the position of the seat, and suggests relating the position of the seat at which the knee bending angle becomes an appropriate angle to a parameter corresponding to the user's height, but does not provide a theory about how to change the seat position with respect to the user's height in order to achieve a desired knee bending angle. Consequently, in the composition described in Patent Document 2, it is not clear how the user's height and the position at which the user's buttocks are supported by the seat are related in order to set the knee bending angle to a desired angle.